In the manufacture of tissue and towel products, a common step is the creping of the product. This creping is done to provide desired aesthetic and performance properties to the product. Many of the aesthetic properties of tissue and towel products rely more upon the perceptions of the consumer than on properties that can be measured quantitatively. Such things as softness, and perceived bulk are not easily quantified, but have significant impacts on consumer acceptance. Since many of the properties of tissue and towel products are controlled or are at least influenced by the creping process, it is of interest to develop methods for controlling the creping process. Although the creping process is not well understood, it is known that changes in the process can result in significant changes in the product properties. A need exists to provide a method for influencing the creping process by allowing the control of the adhesion of the tissue or towel substrate to the surface from which it is creped, most usually large cylindrical dryers known in the industry as Yankee dryers.
Paper is generally manufactured by suspending cellulosic fibers of appropriate length in an aqueous medium and then removing most of the water to form a web. The paper derives some of its structural integrity from the mechanical arrangement of the cellulosic fibers in the web, but most by far of the paper's strength is derived from hydrogen bonding which links the cellulosic fibers to one another. With paper intended for use as bathroom tissue, the degree of strength imparted by this interfiber bonding, while necessary to the utility of the product, results in a lack of perceived softness that is inimical to consumer acceptance. One common method of increasing the perceived softness of bathroom tissue is to crepe the paper. Creping is generally effected by fixing the cellulosic web to a Yankee drum thermal drying means with an adhesive/release agent combination and then scraping the web off of the Yankee by means of a creping blade. Creping, by breaking a significant number of interfiber bonds, increases the perceived softness of resulting bathroom tissue product.
In the past, common classes of thermosetting adhesive resins which have been used as Yankee dryer adhesives have been represented by poly (aminoamide)-epichlorohydrin polymers (hereinafter referred to as PAE resins), such as those polymers sold under the tradenames Kymene, Rezosol, Cascamid, and Amrezs. Each of these materials represent products sold respectively by the Hercules Chemical Company, the Houghton Company, the Borden Company, and Georgia-Pacific. Although these materials are now in commercial use, our novel adhesive formulations are environmental friendly and have lower in-use cost.
This invention provides adhesion which is equal or better than the adhesion characteristics available through the use of PAE resins but having none of the attendant environmental problems associated with the halogen moiety. The halogen free, particularly chloride free, Yankee dryer adhesives of this invention prevent or inhibit chloride or halogen induced corrosion of the Yankee drum surface and, also, are friendly to the environment and have a lower in use cost.
Obtaining and maintaining adhesion of tissue and towel products to Yankee dryers is an important factor in determining crepe quality. Inadequate adhesion results in poor or non-existing creping, whereas excessive adhesion may result in poor sheet quality and operational difficulties. Traditionally, creping adhesives alone or in combination with release agents have been applied to the surface of the dryer in order to provide the appropriate adhesion to produce the desired crepe. Various types of creping adhesives have been used to adhere fibrous webs to dryer surfaces such as Yankee dryers. Some examples of prior art creping adhesives are disclosed in U.S. Pat. Nos. 4,886,579; 4,528,316 and 4,501,640.
U.S. Pat. No. 5,246,544 describes a creping adhesive that provides the ability to control coating mechanical properties and adhesion, and which can be more easily removed from dryer surfaces. The adhesive system described in said patent provides high adhesion of a fibrous web to dryer surface with low "friction". Having low friction means that the fibrous web can easily be removed from the dryer surface. Other references of interest include U.S. Pat. No. 5,232,553 and 4,684,439. All the prior art patents are of interest but do not diclose polymers having at least one primary or secondary amine group in the backbone such as chitosan, polyvinylamine, polyvinyl alcohol-vinyl amine, polyaminoamide and etc., in combination with the dialdehydes or the zirconium crosslinking compounds having a valence of plus four such as ammonium zirconium carbonate, zirconium acetylacetonate, zirconium acetate, zirconium carbonate, zirconium sulfate, zirconium phosphate, potassium zirconium carbonate, zirconium sodium phosphate and sodium zirconium tartrate. These patents also do not relate to creping adhesives or the creping of tissue and towel from a Yankee dryer. U.S. Pat. Nos. 5,374,334 and 5,382,323 relate to adhesives reacted with the crosslinking agent prior to establishing contact with the Yankee surface. In our novel process the crosslinking agents are either charged to the Yankee surface at the same time as the adhesive polymer or are mixed shortly prior to charging the polymer and crosslinking agent mixture to the Yankee surface without reacting the crosslinking agent with the polymer.